Cationic cluster formation versus disproportionation of low-valent indium and gallium complexes of 2,2′-bipyridine

Group 13 M-I compounds often disproportionate into M-0 and M-III. Here, however, we show that the reaction of the M-I salt of the weakly coordinating alkoxyaluminate [Ga-I(C6H5F)(2)](+)[Al(ORF)(4)](-) (R-F = C(CF3)(3)) with 2,2'-bipyridine (bipy) yields the paramagnetic and distorted octahedral [Ga(bipy)(3)](2+center dot){[Al(ORF)(4)](-)}(2) complex salt. While the latter appears to be a Ga-II compound, both, EPR and DFT investigations assign a ligand-centred [Ga-III{(bipy)(3)}(center dot)](2+) radical dication. Surprisingly, the application of the heavier homologue [(I)n(I)(C6H5F)(2)](+)[Al(ORF)(4)](-) leads to aggregation and formation of the homonuclear cationic triangular and rhombic [In-3(bipy)(6)](3+), [In-3(bipy)(5)](3+) and [In-4(bipy)(6)](4+) metal atom clusters. Typically, such clusters are formed under strongly reductive conditions. Analysing the unexpected redox-neutral cationic cluster formation, DFT studies suggest a stepwise formation of the clusters, possibly via their triplet state and further investigations attribute the overall driving force of the reactions to the strong In - In bonds and the high lattice enthalpies of the resultant ligand stabilized [M-3](3+){[Al(ORF)(4)](-)}(3) and [M-4](4+){[Al(ORF)(4)](-)}(4) salts.